JP6493289B2 - Sheet stacking apparatus, sheet post-processing apparatus including the same, and image forming apparatus - Google Patents

Description

  The present invention is used in an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and a sheet post-processing apparatus that performs post-processing such as punch hole forming processing and binding processing on a sheet of paper or the like image-formed by the image forming apparatus. The present invention relates to a sheet stacking apparatus, a sheet post-processing apparatus including the same, and an image forming apparatus.

  An electrophotographic image forming apparatus irradiates a peripheral surface of an image carrier (photosensitive drum) with light based on image information read from an original image or image information transmitted from an external device such as a computer. An electrostatic latent image is formed. After the toner is supplied from the developing device to the electrostatic latent image to form a toner image, the toner image is transferred to a sheet. The paper after the transfer process is subjected to a toner image fixing process and then discharged onto a discharge tray from the sheet discharge unit.

  In such an image forming apparatus, a method of notifying the full state when the number of discharged sheets reaches a preset stackable number is known in order to detect the full state of sheets discharged onto the discharge tray. ing. Here, when the discharged paper is a large size, the weight is larger than that of the small size. Therefore, the number of sheets that can be stacked is reduced in consideration of the durability of the discharge tray. Therefore, it is necessary to set the number of sheets that can be stacked differently between the small size paper and the large size paper. However, for example, when the stacking height increases due to continuous printing of images with a high printing rate, the discharge tray may become full before reaching the stackable number of sheets.

  As another method of detecting the paper full status, a load detection sensor is provided to detect the stack height of the paper discharged on the output tray, and the paper full status on the output tray is based on the detection result of the load detection sensor. There is a known method for detecting this. As the stacking detection sensor, a transmission type optical sensor having a light receiving portion and a light emitting portion in the paper width direction is widely used. However, since the large size paper is difficult to slide down along the inclination of the discharge tray, the position of the upper surface of the paper is more likely to fluctuate than the small size paper. In the case of a transmission type optical sensor, it is possible to detect a sheet only at a preset stacking height. For this reason, there is a problem that a small-size and a large-size load detection sensor are separately required, leading to an increase in cost.

  Therefore, Patent Document 1 has a distance measuring sensor that detects the uppermost surface of the sheet, and the sheet is detected when the height of the uppermost surface of the stacked sheets is continuously detected a plurality of times. Discloses a sheet processing apparatus that is determined to be full.

  Patent Document 2 discloses a sheet processing apparatus that determines that a sheet is full when the weight of the sheet stacked on the sheet stacking unit reaches a predetermined amount and stops stacking the sheet. ing. Specifically, the lifting time when the stack tray (sheet stacking means) is full of sheets is stored, and the actual rising time is slower than the rising time when the sheets are full or the actual falling time is when the sheets are full. If it is faster than the descent time, it is determined that the sheets stacked on the stack tray are over full.

JP-A-11-322187 JP 2007-15824 A

  However, in the method of Patent Document 1, it is necessary to repeat the raising / lowering operation of the discharge tray a plurality of times in order to detect the full sheet state, and there is a problem that sheet discharge efficiency and stacking efficiency are deteriorated. Further, in the method of Patent Document 2, since the weight at the time of full load varies depending on the type of sheet (weight per unit area) and the printing rate, there are cases where the full state of the sheet cannot be detected accurately.

  In view of the above problems, an object of the present invention is to provide a sheet stacking apparatus capable of appropriately setting the number of sheets that can be stacked on a sheet stacking unit, a sheet post-processing apparatus including the sheet stacking apparatus, and an image forming apparatus. To do.

  In order to achieve the above object, a first configuration of the present invention includes a sheet discharge unit, a sheet stacking unit, a first detection mechanism, a driving device, a second detection mechanism, and a control unit. It is a loading device. The sheet discharge unit discharges the sheet. The sheet stacking unit can be moved up and down, and the sheets discharged from the sheet discharge unit are stacked. The first detection mechanism detects the sheet stacking unit or the upper surface of the sheets stacked on the sheet stacking unit. The driving device includes a sheet between the upper surface detection position where the upper surface of the sheet stacking unit or the sheet stacked on the sheet stacking unit is detected by the first detection mechanism and a reference position lowered by a predetermined distance from the upper surface detection position. Raise and lower the loading section. The second detection mechanism detects that the sheet stacking unit is at the reference position. The control unit controls the discharge of the sheet from the sheet discharge unit and the elevation of the sheet stacking unit by the driving device. When the same type of sheets are continuously discharged from the sheet discharge unit, the control unit raises the sheet stacking unit from the reference position to the upper surface detection position in advance and loads the sheet stacking unit according to the rising time of the sheet stacking unit. Set the possible number.

  According to the first configuration of the present invention, the number of sheets that can be stacked in the sheet stacking unit is set according to the rising time of the sheet stacking unit from the reference position to the upper surface detection position. Regardless of this, it is possible to set an appropriate number of sheets that can be stacked with a simple configuration, and it is possible to appropriately manage the sheet stacking amount on the sheet stacking unit.

Schematic showing an internal configuration of a sheet post-processing apparatus 20 provided with an image forming apparatus 100 and a sheet stacking apparatus 60 of the present invention 1 is a partially enlarged view of the sheet post-processing apparatus 20 in FIG. A block diagram showing a control path of an image forming system including the image forming apparatus 100 and the sheet post-processing apparatus 20 The figure which shows a mode that the upper surface position of the paper loaded on the discharge tray 50 is detected using the paper pressing member 51 and the upper surface detection sensor 53. A flowchart showing an example of sheet stacking control in the sheet stacking apparatus 60 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, an image forming system including the image forming apparatus 100 and the sheet post-processing apparatus 20 including the sheet stacking apparatus 60 of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing internal configurations of an image forming apparatus 100 and a sheet post-processing apparatus 20 according to the present invention. In the present embodiment, a digital multi-function peripheral is illustrated as an example of the image forming apparatus 100. However, the paper post-processing apparatus 20 of the present invention is other than a digital multi-function peripheral, for example, a laser printer, an inkjet printer, a facsimile machine, Similarly, it can be connected.

  As shown in FIG. 1, an image forming unit P that forms a monochrome image by each process of charging, exposure, development, and transfer is disposed in the main body of an image forming apparatus (for example, a monochrome multifunction device) 100.

  In the image forming unit P, along the rotation direction of the photosensitive drum 1 (counterclockwise direction in FIG. 1), the charging unit 2, the exposure unit 3, the developing device 4, the transfer roller 7, the cleaning device 8, and the static eliminating device. (Not shown) is provided. In the image forming unit P, the image forming process for the photosensitive drum 1 is executed while rotating the photosensitive drum 1 in the counterclockwise direction in FIG.

  When performing a copy operation, the image reading unit 18 reads the image data of the document and converts it into an image signal. On the other hand, in the image forming portion P, the photosensitive drum 1 that rotates counterclockwise in the drawing is uniformly charged by the charging portion 2. Next, the exposure unit 3 irradiates the photosensitive drum 1 with a laser beam (light beam) on the basis of the document image data read by the image reading unit 18, so that the electrostatic latent image based on the image data is transferred to the photosensitive member. Form on the surface of the drum 1. Thereafter, the developing device 4 attaches toner to the electrostatic latent image to form a toner image.

  A sheet is conveyed from the sheet storage unit 10 through the sheet conveyance path 11 and the registration roller pair 13 at a predetermined timing toward the image forming unit P on which the toner image is formed as described above. The toner image on the surface of the photosensitive drum 1 is transferred onto the sheet by the transfer roller 7. The sheet on which the toner image has been transferred is separated from the photosensitive drum 1, conveyed to the fixing unit 9, and heated and pressed to fix the toner image on the sheet.

  The sheet that has passed through the fixing unit 9 is discharged to the in-body discharge space 16 through the sheet conveyance path 11 and the discharge roller pair 14. The paper discharged by the discharge roller pair 14 is carried into a paper post-processing device 20 mounted in the in-body paper discharge space 16.

  FIG. 2 is a side sectional view of the sheet post-processing apparatus 20. Inside the sheet post-processing device 20, a punch hole forming device 21 that forms punch holes on the loaded paper, a processing tray 30 that stacks a plurality of loaded paper, and a processing tray 30 are provided. A stapler 40 is provided for binding the stacked paper bundle with staples. A discharge tray 50 that can be moved up and down to a position suitable for paper discharge is provided on the side surface of the paper post-processing device 20.

  The punch hole forming device 21 is disposed in the upper part of the paper post-processing device 20 and forms a plurality of punch holes along one side edge (the front or rear side of the device) parallel to the paper transport direction. At the substantially central portion of the upstream side of the punch hole forming device 21 and the direction orthogonal to the paper transport direction (the direction perpendicular to the paper surface of FIG. 2), A carry-in detection sensor (not shown) for detecting the tip is arranged.

  A first discharge roller pair 27 is disposed on the downstream side of the punch hole forming device 21 with respect to the paper transport direction. On the upstream side of the first discharge roller pair 27, an actuator type paper detection sensor 28 for detecting the passage of paper is disposed.

  Further, below the first discharge roller pair 27, a processing tray 30 on which a predetermined number of sheets conveyed by the first discharge roller pair 27 are aligned and stacked, and a bundle of sheets stacked on the processing tray 30 (sheet bundle) ) Is provided with a stapler 40 for performing the binding process.

  A second discharge roller pair 29 that discharges the sheet bundle from the processing tray 30 to the discharge tray 50 is disposed on the downstream side of the processing tray 30 with respect to the sheet conveyance direction. The second discharge roller pair 29 includes a rubber discharge roller 29a that can be rotated forward and backward by a drive motor (not shown), and a resin discharge roller 29b that rotates following the discharge roller 29a. . The discharge roller 29a is supported by a roller holder 31 that can swing up and down about the rotation shaft 31a.

  On the downstream side of the first discharge roller pair 27 (on the left side in FIG. 2) above the processing tray 30, the paper carried by the first discharge roller pair 27 is struck in the direction of the processing tray 30 to be along the tray surface. A hitting member 33 is provided. The processing tray 30 is provided so as to incline downward toward the rear end side (the right side in FIG. 2) of the stacked paper, and the second discharge roller pair 29 is rotated in the reverse direction so that the paper is removed from the rear end side. The paper is drawn onto the processing tray 30, and the rear end of the paper comes into contact with the abutting portion 30a. As a result, the sheets are stacked on the processing tray 30 with the rear ends thereof aligned. Further, the processing tray 30 is provided with a pair of side end alignment cursors 35 for aligning the sheet bundle loaded on the processing tray 30 in the width direction (direction perpendicular to the paper surface of FIG. 2).

  The stapler 40 can be moved in the paper width direction perpendicular to the transport direction by a moving mechanism (not shown), and moves to a predetermined position along the abutting portion 30a of the processing tray 30 according to the content of the binding process.

  Next, the operation of the sheet post-processing apparatus 20 will be described. When a sheet on which image forming processing has been performed by the image forming apparatus 100 is carried in and punch hole formation is instructed, a predetermined position (for example, a side edge on the front side of the apparatus) of the sheet conveyed by the punch hole forming apparatus 21 If punch holes are formed at two locations along the edge) and punch hole formation is not instructed, the punch hole forming device 21 is passed through.

  Then, the sheet is conveyed further downstream by the first discharge roller pair 27. At this time, as shown in FIG. 2, the roller holder 31 swings upward, and the discharge roller 29a is disposed at a position (separated position) separated from the discharge roller 29b. Therefore, the sheet conveyed by the first discharge roller pair 27 protrudes to the discharge tray 50 through the gap between the discharge roller 29a and the discharge roller 29b.

  At the timing when the trailing edge of the sheet passes through the first discharge roller pair 27, the roller holder 31 is swung downward and the discharge roller 29a is disposed at a position (contact position) where the discharge roller 29a contacts the discharge roller 29b. Thereafter, the tapping member 33 is driven to cause the paper to follow the processing tray 30. In this state, by rotating the discharge roller 29a in the reverse direction (counterclockwise direction in FIG. 2), the paper is drawn along the processing tray 30, and the trailing edge is aligned by the abutting portion 30a. At this time, the intermediate portion of the sheet is nipped by the second discharge roller pair 29, and the leading end of the sheet protrudes from the second discharge roller pair 29 onto the discharge tray 50.

  When the acceptance of one bundle of sheets is completed, the stapler 40 is moved to the notch position of the abutting portion 30a to insert the trailing end of the bundle of sheets into the staple unit 40a, and the staple unit 40a binds the bundle of sheets. Is done. After the sheet bundle is bound by the staple unit 40 a, the sheet bundle is conveyed upward along the processing tray 30 by rotating the second discharge roller pair 29 in the forward direction, and is discharged onto the discharge tray 50.

  When shift discharge is set, when the second discharge roller pair 29 is driven to discharge the sheet bundle to the discharge tray 50, the roller holder 31 is first moved to the separation position. Thereafter, the side edge alignment cursor 35 is disposed at a position (shift position) shifted by a predetermined amount in a position (reference position) at which the sheet is received or in a direction orthogonal to the discharge direction (sheet width direction) from the reference position. Then, the roller holder 31 is moved to the contact position to discharge the paper. As a result, the sheet bundle is alternately discharged to a reference discharge position on the discharge tray 50 and a shift discharge position shifted by a predetermined amount from the reference discharge position in a direction orthogonal to the discharge direction (paper width direction). On the discharge tray 50, they are alternately stacked in the paper width direction and sorted.

  A sheet pressing member 51 is disposed below the second discharge roller pair 29. The sheet pressing member 51 is supported so as to be swingable about the fulcrum 51a, and overlaps the discharge tray 50 and a retreat position where it is retracted from the discharge tray 50 (not overlapping the discharge tray 50) as shown in FIG. It is selectively arranged at a sheet pressing position that protrudes to the position and presses the upper surface of the sheet discharged onto the discharge tray 50.

  Further, the sheet pressing member 51 constitutes an upper surface detection mechanism 55 that detects the upper surface position of the sheets stacked on the discharge tray 50 in a state of being disposed at the sheet pressing position. The upper surface detection mechanism 55 includes a sheet pressing member 51 and an upper surface detection sensor 53 (see FIGS. 3 and 4) disposed in the vicinity of the sheet pressing member 51.

  FIG. 3 is a block diagram illustrating a control path of the image forming system including the image forming apparatus 100 and the sheet post-processing apparatus 20. Note that the control unit 70 itself is complicated because various controls of each part of the apparatus are performed in using the image forming system. Therefore, in FIG. 3, portions of the control unit 70 and the sheet post-processing device 20 that are necessary for carrying out the present invention are mainly described. Here, the entire image forming system is controlled using the control unit 70 provided in the image forming apparatus 100, but a control unit may be provided in the sheet post-processing apparatus 20.

  The upper surface detection sensor 53 is a PI (photo interrupter) sensor provided with a detection unit including a light emitting unit and a light receiving unit. Hereinafter, a method for detecting the upper surface position of the sheets stacked on the discharge tray 50 will be described with reference to FIG.

  When the sheet pressing member 51 is moved from the retracted position (position A in FIG. 4) retracted to the inside (right side in FIG. 4) of the side surface 20a of the sheet post-processing device 20 to the sheet pressing position overlapping the discharge tray 50 If the front end of the pressing member 51 does not contact the paper on the discharge tray 50 or the upper surface of the discharge tray 50, the pressing member 51 is disposed at the protruding position (position B in FIG. 4). At this time, the light reception signal level of the detection unit of the upper surface detection sensor 53 is in a HIGH state. The sheet pressing member 51 can swing between a retracted position and a protruding position.

  When sheets are stacked on the discharge tray 50, the sheet pressing member 51 is pressed against the upper surface of the sheet and swings, and rotates clockwise from the protruding position in FIG. As a result, the light path of the detection unit of the upper surface detection sensor 53 is blocked by the light shielding plate formed on the sheet pressing member 51, and the light reception signal level of the detection unit is switched from HIGH to LOW. This position (position C in FIG. 4) is the upper surface detection position.

  The lower limit position detection sensor 59 detects whether or not the discharge tray 50 is disposed at the lower limit position. The lower limit position detection sensor 59 is a PI sensor similar to the upper surface detection sensor 53, and the light path of the detection unit of the lower limit position detection sensor 59 is blocked by a light shielding plate (not shown) formed on the discharge tray 50. It is possible to detect that the discharge tray 50 is at the lower limit position by switching the received light signal level from HIGH to LOW.

  The control unit 70 includes a central processing unit (CPU) 71 as a central processing unit, a read only memory (ROM) 72 that is a read-only storage unit, a random access memory (RAM) 73 that is a readable / writable storage unit, A temporary storage unit 74 for storing image data and the like, a counter 75, and a plurality (two in this case) of I / Fs (interfaces) 76 are provided.

  The ROM 72 stores data that cannot be changed, such as system control programs and numerical values necessary for control. The RAM 73 stores necessary data generated during system control, data temporarily required for control, and the like. The ROM 72 (or RAM 73) also stores a regulation number setting table that stores the ascending time of the discharge tray 50 and the stackable number N1 of the discharge tray 50 in association with each other.

  The timer 77 measures the drive time of the tray drive motor 57 that drives the discharge tray 50 (the rise time of the discharge tray 50) in sheet stacking control to be described later.

  The counter 75 counts the number of sheets printed in the image forming apparatus 100 and counts the number of sheets carried into the sheet post-processing apparatus 20 from the image forming apparatus 100 based on a detection signal from the carry-in detection sensor. Alternatively, the number of sheets carried on the processing tray 30 is counted based on the detection signal of the sheet detection sensor 28 disposed on the upstream side of the processing tray 30 with respect to the sheet conveyance direction. Note that the number of times may be stored in the RAM 73, for example, without providing the counter 75 separately.

  In addition, the control unit 70 transmits a control signal from the CPU 71 to the respective units and apparatuses in the system including the image forming apparatus 100 and the sheet post-processing apparatus 20 through the I / F 76. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 71 through the I / F 76. Examples of each part and device controlled by the control unit 70 include a paper transport unit 17 including a paper storage unit 10, a registration roller pair 13, a discharge roller pair 14, etc. (all of which are shown in FIG. 1) of the image forming apparatus 100. Reading unit 18, image forming unit P, fixing unit 9, punch hole forming device 21 of paper post-processing device 20, first discharge roller pair 27, second discharge roller pair 29, processing tray 30, stapler 40, discharge tray 50, Examples thereof include a tray drive motor 57. Note that the second discharge roller pair 29, the discharge tray 50, the upper surface detection mechanism 55, the tray drive motor 57, and the lower limit position detection sensor 59 together with the control unit 70 constitute the sheet stacking device 60 of the present invention.

  The operation unit 80 is provided with a liquid crystal display unit 81, LEDs 82 indicating various states, and a numeric keypad 83. The user operates the operation unit 80 to input an instruction, whereby the image forming apparatus 100, paper post-processing is performed. Various settings of the apparatus 20 are performed, and various functions such as an image forming function and a post-processing function are executed. The liquid crystal display unit 81 displays the system status, displays the image formation status and the number of prints, and can be used as a touch panel for various settings such as functions such as double-sided printing and black-and-white reversal, magnification setting, and density setting. .

  FIG. 5 is a flowchart showing an example of sheet stacking control in the sheet stacking apparatus 60 of the present invention. The sheet stacking procedure in the sheet stacking apparatus 60 of the present invention will be described along the steps of FIG. 5 with reference to FIGS. FIG. 5 shows sheet stacking control when a large size (A3 size) sheet is stacked.

  In the paper stacking control shown in FIG. 5, in a series of printing operations (one job) for performing continuous printing (continuous discharge), the paper on the discharge tray 50 according to the rising time of the discharge tray 50 from the lower limit position (reference position). Set the number of sheets that can be loaded.

  When the user inputs a print instruction from the operation unit 80 (see FIG. 3) or the personal computer setting screen (operation terminal), the control unit 70 starts detecting the upper surface by the paper pressing member 51. Specifically, the control unit 70 arranges the paper pressing member 51 at the detection position (paper pressing position) (step S1). In this state, the tray drive motor 57 is driven to raise the discharge tray 50 from the lower limit position. When the upper surface of the discharge tray 50 is detected by a detection signal from the upper surface detection sensor 53, the tray drive motor 57 is stopped. Thereby, the discharge tray 50 is raised to the upper surface detection position (step S2). Further, the rising time T of the discharge tray 50 is measured by the timer 77 (step S3).

  Next, the control unit 70 determines whether or not the measured rise time T is less than or equal to a reference time T1 (for example, 1 second) (step S4). If T ≦ T1 (Yes in step S4), it is determined that the paper on the discharge tray 50 is full (step S5), the printing operation is interrupted, and the paper loaded on the discharge tray 50 is loaded. A notification requesting to be removed is made (step S6). This notification is performed by displaying a message on the liquid crystal display unit 81 of the operation unit 80, for example.

  Then, it is determined whether or not the sheets stacked on the discharge tray 50 have been removed (step S7). If the sheets have been removed (Yes in step S7), the discharge tray 50 is lowered to the lower limit position (step S7). Step S8), returning to step S1. On the other hand, if the sheet is not removed (No in step S7), the notification requesting to remove the sheet is continuously performed with the discharge tray 50 stopped at the upper surface detection position.

  Note that whether or not the sheets stacked on the discharge tray 50 have been removed can be determined as follows. With the paper pressing member 51 moved to the detection position, the discharge tray 50 is raised and the upper surface of the paper is detected by the detection signal from the upper surface detection sensor 53. And the discharge tray 50 is stopped in the position which detected the upper surface. At this time, the sheet is sandwiched between the discharge tray 50 and the sheet pressing member 51.

  When the paper stacked on the discharge tray 50 is removed (the upper surface position is lowered), the paper pressing member 51 swings counterclockwise, and the detection state of the upper surface detection sensor 53 changes. It can be recognized that the paper stacked on the top has been removed.

  On the other hand, if T> T1 (No in step S4), the stackable sheet number N1 is set according to the rising time T (step S9). Note that the discharge tray 50 is disposed at the lower limit position in the default state, and the number of sheets that can be stacked corresponding to the rising time T until the upper surface of the discharge tray 50 in a state in which no sheets are normally stacked reaches the upper surface detection position. N1 is set. Further, when the sheet remains on the discharge tray 50, the stackable sheet number N1 corresponding to the rising time T until the upper surface of the sheet reaches the upper surface detection position is set. That is, as the number of sheets stacked on the discharge tray 50 increases, the rising time T of the discharge tray 50 becomes shorter. Therefore, the longer the rising time T, the larger the number of stackable sheets N1 is set. For example, if the rising time T is longer than 1 second and 2 seconds or less, N1 = 100 (sheets). If it is longer than 2 seconds and 3 seconds or less, N1 = 200 (sheets). If it is longer than 3 seconds, N1. = 300 (sheets).

  Thereafter, the paper is discharged onto the discharge tray 50 by starting printing (step S10). At this time, the sheet pressing member 51 moves to a retracted position that does not interfere with sheet discharge while the sheet is being discharged, and moves to the sheet pressing position when the discharged sheet is stacked on the discharge tray 50. Repeat for each sheet of paper. Then, the control unit 70 gradually lowers the discharge tray 50 from the upper surface detection position in accordance with the increase in the number of sheets stacked by the detection signal from the upper surface detection sensor 53. Further, the counter 75 counts the number of sheets stacked on the discharge tray 50 (the number of discharged sheets) N (step S11).

  Next, the control unit 70 determines whether or not the number of stacked sheets N counted by the counter 75 is equal to or greater than the stackable number N1 (step S12). If N <N1 (No in step S12), the paper discharge is continued as it is. Even when it is detected that the sheets stacked on the discharge tray 50 in the state of N <N1 are removed, the discharge of the sheets is continued until N ≧ N1.

  On the other hand, if N ≧ N1 (Yes in step S12), it is determined that the discharge tray 50 is fully loaded, and the paper discharge is stopped (step S13). Thereafter, the process proceeds to step S8, the discharge tray 50 is lowered to the lower limit position (step S8), the process returns to step S1, and the same procedure is repeated thereafter.

  On the other hand, when stacking small size (A4 size) sheets on the discharge tray 50, stacking of sheets is started in a state where the discharge tray 50 is raised to the upper surface detection position. Then, as the number of stacked sheets increases, the discharge tray 50 is lowered, and when reaching the lower limit position, it is determined that the paper on the discharge tray 50 is full, and the paper discharge is stopped. A notification requesting that the sheets stacked on the printer be removed is issued.

  By performing the control as described above, an appropriate stackable sheet number N1 is set according to the rising time T from the lower limit position of the discharge tray 50 to the upper surface detection position. This allows the user to remove the paper before the upper surface of the paper rises to a position where the paper stacked on the discharge tray 50 and the paper discharged by the second discharge roller pair 29 may collide. A reminder can be made. Accordingly, the sheets stacked on the discharge tray 50 are not pushed out in the discharge direction by the subsequent sheets, and it is possible to effectively prevent the sheet from being misaligned on the discharge tray 50 and falling from the discharge tray 50.

  When the number of discharged sheets reaches the stackable number N1, the discharge of the sheets is stopped and the discharge tray 50 is once lowered to the lower limit position and then raised again to the upper surface detection position. Thus, the stackable sheet number N1 is reset. Thereby, for example, even when the user removes a part or all of the sheets stacked on the discharge tray 50, the stackable sheet number N1 corresponding to the removed sheet number is determined. Accordingly, it is possible to set an appropriate stackable sheet number N1 regardless of the sheet stacking amount on the discharge tray 50, and it is possible to appropriately manage the sheet stacking amount on the discharge tray 50. Furthermore, even if the paper is removed before the number of sheets discharged reaches the stackable number N1, the sheet discharge is continued until the number of stackable sheets N1 is reached, so that the sheet discharge is unnecessarily stopped. Also disappear.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the sheet stacking device 60 that stacks the sheets discharged from the sheet post-processing device 20 connected to the image forming apparatus 100 has been described as an example. However, the sheets are discharged from the image forming apparatus 100. The present invention can also be applied to a sheet stacking apparatus that stacks sheets.

  Further, in the above embodiment, the paper stacking control based on the rising time of the discharge tray 50 is applied only to the large size paper (A3 size), but can be similarly applied to the small size paper (A4 size). . In this case, by setting the stackable sheet number N1 set based on the rising time T to be larger than that of the large size sheet, it is possible to perform appropriate sheet stacking control according to the sheet size. Also, if the stackable number N1 is changed according to not only the size of the paper but also the thickness, basis weight (basis weight) of the paper, the printing rate of the image to be printed, etc. Appropriate paper loading control can be performed.

  The present invention can be used in a sheet stacking apparatus that stacks sheets discharged from the sheet discharge unit. By using the present invention, when stacking a plurality of types of sheets, a sheet stacking device capable of reliably detecting the full state of the sheet stacking unit without providing a plurality of stacking detection sensors, and a sheet post-processing device including the same In addition, an image forming apparatus can be provided.

20 Paper post-processing device (sheet post-processing device)
21 Punch hole forming device 27 First discharge roller pair 28 Paper detection sensor 29 Second discharge roller pair (sheet discharge unit)
30 processing tray 40 stapler 50 discharge tray (sheet stacking section)
51 Paper pressing member 53 Upper surface detection sensor 55 Upper surface detection mechanism (first detection mechanism)
57 Tray drive motor (drive device)
59 Lower limit position detection sensor (second detection mechanism)
60 Sheet stacking apparatus 70 Control unit 100 Image forming apparatus

Claims (8)

A sheet discharge unit for discharging the sheet;
A sheet stacking unit capable of moving up and down, on which sheets discharged from the sheet discharge unit are stacked;
A first detection mechanism for detecting an upper surface of the sheet stacking unit or the sheets stacked on the sheet stacking unit;
Between the upper surface detection position where the upper surface of the sheet stacking unit or the sheet stacked on the sheet stacking unit is detected by the first detection mechanism, and the reference position lowered by a predetermined distance from the upper surface detection position A driving device for raising and lowering the sheet stacking unit;
A second detection mechanism for detecting that the sheet stacking unit is at the reference position;
A control unit for controlling discharge of the sheet from the sheet discharge unit and raising and lowering of the sheet stacking unit by the driving device;
With
When the same type of sheets are continuously discharged from the sheet discharge unit, the control unit raises the sheet stacking unit from the reference position to the upper surface detection position in advance, and responds to the rising time of the sheet stacking unit. To set the number of sheets that can be stacked in the sheet stacking unit ,
When the number of sheets stacked on the sheet stacking unit reaches the stackable number, the control unit lowers the sheet stacking unit to the reference position and then raises the sheet stacking unit to the upper surface detection position. The sheet stacking apparatus is characterized in that when the rising time is equal to or shorter than a predetermined time, the discharge of the sheet from the sheet discharge unit is stopped .   2. The sheet stacking apparatus according to claim 1, wherein the control unit changes the number of sheets that can be stacked according to a type of a sheet discharged from the sheet discharge unit. 2. The control unit according to claim 1 , wherein when the rising time of the sheet stacking unit is longer than the predetermined time , the control unit resets the stackable sheet number according to the rising time of the sheet stacking unit. Item 3. The sheet stacking apparatus according to Item 2. 4. The control unit according to claim 1 , wherein when the rising time of the sheet stacking unit is equal to or shorter than the predetermined time, the control unit issues a notification prompting removal of the sheets stacked on the sheet stacking unit. The sheet stacking apparatus according to any one of the above. The control unit lowers the sheet stacking unit to the reference position when the lowering of the upper surface position of the sheet is detected by the first detection mechanism after stopping the discharge of the sheet from the sheet discharge unit. together it is increased to the upper surface detection position after the sheet stacking apparatus according to any one of claims 1 to 4, characterized in that resetting the stackable number of sheets in accordance with the rise time of the sheet stacking portion. When the first detection mechanism detects a decrease in the upper surface position of the sheet until the number of sheets stacked on the sheet stacking unit reaches the stackable number of sheets , the control unit sheet stacking apparatus according to any one of claims 1 to 5 the number of the stacked sheets is characterized by continuing the discharge of the sheet from the sheet discharge unit until reaching the stackable number of sheets. A sheet post-processing apparatus comprising the sheet stacking apparatus according to claim 1 . Image forming apparatus including a sheet stacking apparatus according to any one of claims 1 to 6.

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